Such safety switches may be used to monitor movable protective devices such as doors, covers, gratings, and the like of machines and assemblies. When the protective device is opened, the safety switch generally interrupts one or more electric circuits, transferring the associated machine to a safe operating state. For example, the machine is switched off, or starting of the machine is prevented.
Wide use is made of safety switches in which an actuator, generally rigidly connected to the protective device, may be introduced into a reading head of the housing of the safety switch. Introduction of the actuator customarily requires in any event partial positive locking of actuator to reading head, and directly or indirectly effects switching of the safety switch by mechanical coupling elements. Such positive locking represents a kind of mechanical coding so that the safety switch may be actuated only by a predetermined actuator. The protective device may be locked by locking the actuator in the reading head. The locking may, for example, be electromechanically drivable and/or electromechanically unlockable.
DE 43 28 297 C1 discloses a safety switch in which the switching tappet is at the same time configured as armature of the electromagnet actuating the locking mechanism.
DE 697 775 T2 discloses a safety switch in which the actuator may be mechanically locked in the safety switch. A locking slide is displaceable transversely to the longitudinal axis of the switching tappet, is guided in the housing of the safety switch, is electromagnetically actuatable, and may be brought into blocking engagement with the switching tappet below the reading head. The locking slide operates in conjunction with the electromagnetic drive by a coupling device with a reversible actuating ramp. The reversibility of the actuating ramp makes it possible to predetermine whether the locking takes place with the electromagnetic drive voltage-free or under voltage (NORMALLY LOCKED or NORMALLY UNLOCKED).
DE 697 07 081 t2 discloses a safety switch in which the reading head may be fixed to the housing of the safety switch in various predetermined angular positions.
Other such or similar safety switches are disclosed in DE 33 09 372 C2, DE 199 19 949 A1, DE 3429647 C2, and DE 3923663 A1.
Safety switches of a modified type include a reading head and an actuator, each having a first and/or second module with electric and/or electronic components. The components may be caused to interact without electric contact, and accordingly, control the safety switch, are disclosed in DE 197 11 588 A1, for example.
After assembly, the actuator in the reading head may be locked by mechanical means, and as a result, the protective device may be locked. On the basis of the state of the art, the locking takes place, for example, by extension of a tappet in the reading head through an opening in the actuator. In order that the locking forces required, of N for example, may be applied, as a function of the application, the locking system and accordingly the safety switch must be of suitable rugged design.
The actuator is introduced into a channel formed by the reading head. In fouling environments, such as in the vicinity of metal-cutting machine tools, the fouling of the safety switch and of the locking system which occurs may impair preparation of high locking forces and other functions as well.
DE 199 53 898 A discloses an access protection device in which the locking system consists of a magnetic circuit which comprises a magnetizable yoke positioned on the movable component and a U-shaped magnet which may be locked on the yoke. The magnetic action of the magnet may be switched on and off.